Fabrication of Resonance Frequency-Based Sensors for Safeguarding Heritage Documents

Recently, some studies have been reported on using resonance frequency (R_f) based sensors on the micro-strip patch antenna (MPA) concept for safeguarding structural and non-structural components with heritage importance. But hitherto, little has been reported on the health monitoring of heritage documents using MPA. In this study, a strawboard cover of 400 × 320 × 3 mm³ was selected as a representative of a heritage document (having a mass (m) of 336 g and density (ρ) of 379.859 kg/m³), on which a sensing capability (based on MPA) has been introduced. A substrate of 84.58 × 83 mm×3mm³ of 8 g was cut from the strawboard cover based on simulated results per high-frequency structure simulator (HFSS) software, and its R_f characteristics were observed using a Vector network analyzer (VNA). Further, the stimulus effect (moisture and temperature) was ascertained on the substrate for 03 repeated cycles, and a significant shift in the R_f was noticed, which may be calibrated for establishing the health of heritage documents. The results of this study suggest that the dip in R_f (from 2.595 GHz to 1.716 GHz) and rise in effective dielectric constant ( \(\:{\epsilon\:}_{eff})\) (from 2.132 to 4.876) were noticed with an increase in moisture content from (0–10 ml) in the first cycle. A similar trend was observed in the subsequent cycles (post-heating at 50 °C for 10 min).